In accordance with the trend of the high recording density of an HDD, a thin film magnetic head to be mounted is requested to a narrower track width and a narrow gap length and allow high sensitivity. Normally, the thin film magnetic head uses a combination of a write head and a read head. Presently, the mainstream of the read head is a GMR head using the GMR effect. The GMR head is a CIP (Current In Plane) head that supplies an electric signal to a sensor film parallel with a film surface. The need for further improving the recording density promotes the development of a TMR (Tunneling MagnetoResistive effect) and a CPP-GMR (Current Perpendicular to a Plane-Giant MagnetoResistive effect) head that are considered to be advantageous to realizing a high output as well as a narrow track width and a narrow gap length. Unlike conventional GMR heads, the TMR head and the CPP-GMR head are not a CIP-type head that applies a sensing current parallel to the film surface, but a CPP-type head that applies a sensing current perpendicularly to the film surface.
JP-A No. 198000/2003 describes the CPP-GMR that is a CPP-type head. According to this publication, a convex lower lead makes contact with a sensor film. An upper lead is configured to use a smaller width for contact with the sensor film than that needed for the lower lead so as to improve an alignment margin and form a minute contact portion. JP-A No. 298144/2003 describes the head having a convex lower lead similar to that described in JP-A No. 198000/2003. The head uses a flattened convex portion and makes it possible to fabricate a uniform sensor film so as to improve characteristics.
JP-A No. 11449/2005 proposes thinning a domain control film disposed at the side of a sensor and reducing a shield gap. Narrowing the shield gap at the side of the sensor aims at decreasing side-reading. JP-A No. 178656/2004 discloses the structure having the side shield for a similar purpose of reducing side-reading. JP-A No. 332649/2003 aims at magnetic stability of a sensor film and reduction of side-reading. JP-A No. 44490/2005 considers the magnetic stabilization of a pinned layer and proposes forming the pinned layer so that its size in the stripe-height direction becomes greater than the size in the track width.
A CPP-type head uses upper and lower shields as magnetic shields and also uses them as electrodes. An insulating film is disposed on a wall surface of a sensor film. An electrode is disposed over and below the sensor film surface. An electric current is applied perpendicularly to the film surface. In terms of a fabrication process, the track width is first formed, and then the stripe-height is formed. The same applies to JP-A No. 11449/2005 and JP-A No. 44490/2005.
With reference to FIGS. 1 and 2, the following describes an example of the fabrication process of a conventional CPP-type head.
(1-1) First, a sensor film 3 such as a TMR film is formed on a lower shield 1. FIG. (1-1a) is a cross sectional view taken along the ABS line in plan view (1-1b). The same applies to the subsequent diagrams.
(1-2) A track formation resist mask 4 is then formed for forming a track. The track formation resist mask 4 has an opening for an etching area for track forming 41.
(1-3) The track formation resist mask 4 is used as an etching mask to etch the sensor film 3 for the etching area for track forming 41. In order to ensure the insulation of a sensor wall surface, there are formed a second insulating film 5 and a magnetic film 6 functioning as a domain control film. Then, a lift-off process is performed to remove unnecessary parts of the second insulating film 5 and the magnetic film (domain control film) 6. As a result, only the etching area for track forming 41 contains the second insulating film 5 and the magnetic film (domain control film) 6. The second insulating film 5 ensures the insulation in the vicinity of the track.
(1-4) A stripe-height formation resist mask 7 is formed to prescribe the stripe-height direction of the sensor film 3.
(2-1) The stripe-height formation resist mask 7 is used as an etching mask to etch the sensor film 3. The second insulating film 5 and the magnetic film (domain control film) 6 are also etched simultaneously. At this time, etching edges A are formed for the second insulating film 5 and the magnetic film (domain control film) 6.
(2-2) With the stripe-height formation resist mask 7 provided, a first insulating film 8 is formed and is lifted off to leave the first insulating film 8 only at an etched portion of the stripe-height formation resist mask 7.
(2-3) An upper shield 11 is formed.
In the future, it may be necessary to not only improve the recording density, but also to increase a signal frequency. Eventually a narrower gap length may decrease a distance between the upper and lower shields as electrodes to increase the electrostatic capacity between the upper and lower shields as electrodes. Not only the distance, but also an electrode area influences the electrostatic capacity. Increasing the electrode area increases the electrostatic capacity. Increasing the electrostatic capacity may degrade high frequency characteristics. Unlike the CIP head, the CPP-type head uses electrodes for the upper and lower shields. The problem becomes more serious. To avoid this problem, JP-A No. 178656/2004 describes an example of forming another insulating film (gap layer) on an insulating film (equivalent to the second insulating film 5 in FIG. 1) for the track formation portion.
It is known that a fabrication process for forming insulating films uses the lift-off process and the etching process. Such fabrication process greatly influences yields and is empirical in many cases.
For example, let us consider a case of forming an insulating film 10 for the CPP-type head as shown in FIG. 4. FIG. 3 shows an example of using the lift-off process for the fabrication process for forming the insulating film 10. Similarly to FIG. 1, FIG. 3 shows plan views and sectional views.
(3-1) There is shown a diagram after the head is processed in the track-width direction and the stripe-height direction.
(3-2) A resist pattern 9 is formed for forming a third insulating film 10.
(3-3) The third insulating film 10 is formed thereon.
(3-4) The lift-off process is performed to remove unnecessary parts of the third insulating film 10 and the resist pattern 9.
(3-5) The upper shield 11 is formed to complete the head.
The lift-off process is also used for track formation resist mask pattern shapes are disclosed. With respect to the track formation of the CPP-type head structure in accordance with the lift-off process, JP-A No. 332649/2003 discloses the eaves-shaped cross-section whose lift-off pattern has an undercut.
A CPP-type head uses upper and lower shields as magnetic shields and also uses them as electrodes. An insulating film is disposed on a wall surface of a sensor film. An electrode is disposed over and below the sensor film surface. An electric current is applied perpendicularly to the film surface. Vertically applying an electric current may generate an unnecessary electric current path between the upper and lower leads, i.e., a short-circuit or the like. This is undesirable. Decreasing an isolation voltage between the upper and lower leads increases the probability of short-circuit failure occurrence. As a result, this causes a yield to decrease. Eventually a narrower gap length tends to further decreasing a distance between the shields. It is expected to further increase a possibility of causing a short-circuit and decreasing an isolation voltage.
The following problem is suspected when the head is fabricated first in the track-width direction and then in the stripe-height direction as mentioned with reference to FIGS. 1 and 2. After the head is processed in the track-width direction, the insulating film and the domain control film are formed. Then, the head is processed in the stripe-height direction. In this case, the domain control film and the insulating film may be often cut simultaneously. When re-deposition from the lower shield deposits on the insulating film, the lower shield and the domain control film short-circuit. As a result, the short-circuit propagates to the upper shield on the domain control film. Consequently, the lower shield and the upper shield short-circuit.
This will be described in more detail with reference to FIGS. 1 and 2. In (1-3), only the etching area for track forming 41 is provided with the second insulating film 5 and the magnetic film (domain control film) 6. Generally, the second insulating film 5 is very thin such as 10 nm or less in some cases so that the magnetic film (domain control film) 6 can function effectively. The thin second insulating film 5 ensures insulation near the track. In (2-1), the sensor film 3 is etched using the stripe-height formation resist mask 7 as an etching mask. The second insulating film 5 and the magnetic film (domain control film) 6 are etched simultaneously. At this time, etching edges A are formed for the second insulating film 5 and the magnetic film (domain control film) 6. When re-deposition from the lower shield 1 is formed on the second insulating film 5, the lower shield 1 and the magnetic film (domain control film) 6 short-circuit. Part of the reason for the short-circuit is a very small thickness of the second insulating film 5 that is formed simultaneously with the magnetic film (domain control film) 6. As the second insulating film 5 thins, the possibility increases. Thickening the film can decrease the possibility of short-circuiting. In such case, however, the distance between the sensor film and the domain control film increases to degrade the effect of the domain control film and cause a characteristic failure.
Accordingly, it is important to both prevent short-circuiting and stabilize characteristics using the domain control film. It is difficult to find a satisfactory condition for both. When the upper shield 11 is finally formed and the problem described in (2-1) occurs, the lower shield 1 and the upper shield 11 short-circuit to cause a fatal characteristic failure such as decreased output.
When that manufacturing sequence is used to form the head, the width of the magnetic film (domain control film) 6 in the stripe-height direction on the wafer almost equals the sensor film. After lapping of air bearing surface (ABS), the sensor film 3 has a stripe-height of approximately 100 nm to approximately 200 nm. The height becomes much lower than that in a wafer process. That is, the magnetic film (domain control film) 6 also reduces greatly. When a magnetic film such as the magnetic film (domain control film) 6 is subject to reduction in its cubic volume, the magnetic stability degrades. The manufacturing sequence causes the magnetic film (domain control film) 6 to be unstable and may degrade head characteristics. The stripe-height is expected to be much lower and the influence is expected to increase.
A similar problem is expected when a side-shield film is used as the magnetic film 6 instead of the domain control film. The side-shield film needs to absorb an unnecessary magnetic field at a sensor film side. When the head is formed as mentioned above, however, it becomes horizontally long, i.e., very narrow in the stripe-height direction and wide in the track-width direction. In such case, too excessive a shape anisotropy is expected to occur. That is, the side-shield film magnetization may be fixed in the track-width direction to nullify the full functionality of the side shield. As a result, an effect of reducing side-reading degrades to decrease an effect of improving the recording density.
On the other hand, this manufacturing sequence may cause another problem than that mentioned above. This will be described with reference to FIG. 5. FIG. 5 shows that the stripe-height formation resist mask 7 is formed after the track formation. FIG. 5(a) is a plan view. FIG. 5(b) is a cross sectional view taken on the line a-a in FIG. 5(a). It is a common practice to adjust the thickness of the magnetic film 6 (domain control film) during track formation so as to stabilize sensor film characteristics. When the top surface of the magnetic film 6 (domain control film) becomes higher than the sensor film 3 (FIG. 5(b)), a shape defect occurs for the stripe-height formation resist mask 7 that is subsequently formed in region E of FIG. 5(a). The region E in FIG. 5(a) is concave and therefore causes a shape defect for the stripe-height formation resist mask 7 due to a non-uniform thickness in the applied resist film or halation during the photolithography.
When the stripe-height formation resist mask 7 is subject to a shape defect as shown in the drawing, a shape defect occurs in the stripe-height direction of the sensor film 3 and the dimensional accuracy degrades. An edge position in the stripe-height direction of the sensor film 3 becomes a base point to ABS (throat-height zero point) for the read head after the lapping of ABS. The accuracy of this reference position also degrades. Degradation of the reference positional accuracy also leads to degradation of the positional accuracy for a write head to be used in combination. This is because the positional accuracy of a magnetic pole constituting the write head largely depends on the edge positional accuracy in the stripe-height direction of the sensor film 3. When the edge positional accuracy degrades in the stripe-height direction of the sensor film 3, a fluctuation occurs in the length in the stripe-height direction of the magnetic pole constituting the write head after the lapping of ABS. As a result, the write head performance also fluctuates.
It is important to accurately form the stripe-height direction of the read head that specifies the reference position in the stripe-height direction.
The structure in FIG. 1 or 2 can be protected against short-circuiting by forming a third insulating film after processing in the track-width direction and the stripe-height direction and covering the third insulating film up to the inside of an external edge (portion A in 2-1) for the track forming portion. This will be described with reference to FIG. 3. At region B indicated by (3-2), the upper insulating film pattern intersects the outside of the stripe-height forming portion. Halation occurs at that portion to disorder the pattern. This may leave lift-off remainders or cause a shape defect for the upper shield to be formed later.
As shown in FIG. 3, the magnetic film 6 is disposed at the side of the sensor film via the second insulating film 5 during the track width formation. Many structures dispose the side-shield film or the domain control film as the magnetic film 6. According to the structure as shown in FIG. 3, the third insulating film 10 covers the external edge region of the side shield or the domain control film. Therefore, a distance between the magnetic film 6 and the upper shield varies near and away from the sensor. This will be described with reference to FIG. 4. FIG. 4 shows the same state as FIG. 3 (3-5). Since the third insulating film 10 is provided, the distance between the magnetic film 6 (the side-shield film or the domain control film) and the upper shield is small at region C. The distance at region D increases for the thickness of the third insulating film 10. As a result, when the magnetic film 6 is the domain control film, a magnetic flux generated from the domain control film is absorbed into the shield to cause a non-uniform distribution. There may be a possibility of an unfavorable effect such as generation of a magnetic domain wall on the shield and the sensor film. A similar problem may occur when the magnetic film 6 is the side shield. When a distance between the side-shield film and the upper shield varies depending on regions C and D, the side shield causes a non-uniform magnetic action or field distribution in relation to the upper shield. This may adversely affect the side shield and the upper shield.
To improve high frequency characteristics, JP-A No. 178656/2004 mentioned above proposes an example of forming another insulating film (gap layer) on the insulating film (equivalent to the second insulating film in FIG. 1) in the track formation portion. That is, the distance between the upper and lower shields as electrodes is increased to decrease the electrostatic capacity. However, JP-A No. 178656/2004 places stress only on the ABS shape and the side shield structure. Stress is placed only on the ABS shape in terms of the gap layer. There is no mention on processing in the stripe-height direction. When the sensor film is processed for a magnetic head, only processing the track width and the stripe-height can first provide a shape functioning as the sensor. It is very important to establish the structure and the process in consideration for both. The gap layer as disclosed in JP-A No. 178656/2004 makes contact with the upper shield and is preferably smoothly shaped. In many cases, the gap layer has a thickness of several hundreds of nanometers for ensuring an isolation voltage. Stably forming the upper insulating film having such thickness and shape is important for stabilizing shield characteristics and improving an isolation voltage yield. However, JP-A No. 178656/2004 makes no mention of a formation method. Fabricating a stable head remains unclear. JP-A No. 11449/2005 and JP-A No. 44490/2005 provide no description about such insulating film itself.
Methods of forming the insulating film include the lift-off process as shown in FIG. 3. The lift-off process may vary shapes, stability, and ease of fabricating depending on a resist film thickness or constitution. FIG. 3, (3-2) and (3-3), shows the pattern having a vertical wall surface as the resist pattern 9 for forming the third insulating film 10. When this shape is used actually, performing the lift-off process after forming the third insulating film 10 causes lift-off remainders at edges of a boundary between the resist pattern 9 and the third insulating film 10. A shape defect results.
An etching process may be another method of forming the third insulating film. However, the upper surface of the sensor film 3 is also subject to the etching process and may be damaged accordingly. As mentioned above, the lift-off process may be used to form the third insulating film. For example, let us consider that the pattern is used according to the same resist film thickness and shape as for the track formation. Such pattern construction makes the lift-off process difficult if the pattern is used for the process to form the third insulating film. The pattern cannot be used as the resist pattern 9. The reason follows. The track formation is one of finest magnetic head processes. The resist pattern film is very thin and an undercut width is very small.